1. Technical Field
Inflatable medical devices and methods for making and using the same are disclosed. More narrowly, medical invasive balloons, such as those used for transcutaneous heart valve implantation are disclosed. For example, those balloons used for transcatheter aortic-valve implantation.
2. Description of Related Art
Inflatable structures, such as balloons, are widely used in medical procedures. A balloon is inserted, typically on the end of a catheter, until the balloon reaches the area of interest. Adding pressure to the balloon causes the balloon to inflate, in one variation of use, the balloon creates a space inside the body when the balloon inflates.
Balloons may be used in the heart valves, including during Balloon Aortic Valvuloplasty (BAV) and Transcatheter Aortic Valve Implantation (TAVI). The balloons can be used to open a stenosed aortic valve. A stenosed valve may have hard calcific lesions which may tend to tear or puncture a balloon. Additionally, a precise inflated balloon diameter may be desired for increased safety and control.
Balloons may be used to move plaque away from the center of a vascular lumen toward the vasculature walls, such as during an angioplasty or a peripheral vasculature procedure. During this procedure, a balloon tipped catheter is placed in a vascular obstruction. As the balloon is inflated, the vessel constriction is dilated, resulting in improved blood flow.
Two basic types of balloons are utilized: One is a high pressure, low-compliance balloon. The other is a lower pressure, high-compliance balloon.
High-compliance medical balloons are often composed of urethane, latex, silicone, PVC, Pebax, and other elastomers. As the pressure in a high-compliant balloon is increased, the balloon dimensions expand. Once the pressure is reduced, the high-compliance medical balloon may return to its original shape, or near its original shape. High-compliance medical balloons can easily expand several times in volume between zero inflation pressure and burst.
Traditional high-compliance medical balloons can be inadequate for many reasons. High-compliance, or highly elastic medical balloons typically cannot reach high pressures because their walls have a low tensile strength and their walls thin out as the balloon expands. In some instances, high-compliance medical balloons provide insufficient force to complete a procedure. Exceeding the rated pressure of a high-compliance medical balloon creates an excessive risk of balloon failure which can lead to serious complications for the patient.
High-compliance medical balloons also have poor shape control. As a high-compliance medical balloon expands, it may assume a shape dictated mostly by the particulars of the environment inside the patient rather than the clinical goals. In some cases, this can be contrary to what the medical practitioner desires. Many medical procedures are predicated on forming a particular balloon shape reliably.
High-compliance medical balloons often suffer from poor puncture and tear resistance.
Low-compliance, high pressure medical balloons substantially retain their shape under comparatively high pressures. PET (polyethylene terephthalate) is the most common material for use in high pressure low-compliance balloons. PET is commonly used for high-performance angioplasty balloons. PET is stronger than other polymers, can be molded into a variety of shapes and can be made very thin (e.g., 5 μm to 50 μm (0.0002 in. to 0.002 in.)), thus giving these balloons as low profile.
Balloons made from PET walls are fragile and prone to tears. When pressed against a hard or sharp surface in the body, such as stenosis, PET balloons have poor puncture resistance. PET is very stiff so balloons made from PET may be difficult to pack or told into a small diameter and may have poor trackability i.e., the ability to slide and bend over a guidewire deployed through a tortuous vessel).
Balloons made from PET, while stronger than most other balloons made from homogenous polymers, may still not be strong enough to hold pressures sufficient to complete certain medical procedures. Additionally, with a large balloon diameter (For example, 20 mm or greater), a PET balloon still has excessive compliance for procedures such as BAV and TAVI.
PET, like most low compliance balloons, is usually blow-molded. The blow molding process makes it difficult or impossible to create certain shapes. Blow molding can result in wall thicknesses in the balloon that do not match the material thicknesses to the expected load.
Nylon balloons are an alternative material for low-compliance, high pressure balloons. These balloons are typically weaker than PET balloons and so can contain less pressure. Nylon readily absorbs water, which can have an adverse affect on Nylon's material properties in some circumstances. Nylon has improved puncture resistance over PET and is more flexible than PET.
A balloon is desired that can sustain high pressures, provide precise shape control and be highly resistant to tear and puncture.